The invention relates to data communication, and, more particularly, to a low-density parity-check (LDPC) hard decision decoder for high speed wireless data communications.
Recently, high-order modulation formats, such as M-PSK and M-QAM (quadrature amplitude modulation), have been proposed for optical transmission systems to obtain higher spectral efficiency. Moreover, coherent systems are gaining interest due to the availability of high-speed signal processing and low-priced components, as well as the partly relaxed receiver requirements at high data rates. Coherent receivers can exploit all optical field parameters (amplitude, phase, frequency and polarization) in the electrical domain and permit to reach the ultimate limits of spectral efficiency. On the other hand, recent works have also considered applications of turbo and LDPC codes to optical communications. These codes offer capacity approaching performance when the codeword length is very large.
The very-high information rate that needs to be sustained by the emerging optical transmission systems, e.g., 40-100 Gb/s, poses a severe complexity constraint on the decoder. The soft decoding techniques that are traditionally associated with turbo or LDPC codes may be too complex for such systems. LDPC hard decoding methods include the majority-based (MB) time-invariant decoding algorithms, the probabilistic flipping algorithms and several switch-type hybrid algorithms. On the other hand, although a Gallager decoding method B (GB) is optimal for decoding infinite-length codes, it suffers performance degradation when decoding finite-length codes. Expanded optimal switch algorithms for regular codes have been proposed, which provide significant performance improvement over GB. However, for irregular codes, the existing hard decoding algorithms require the degree information of variable nodes. Such requirement significantly increases the circuit level implementation complexity due to the operations of storing and retrieving the degree information.
Accordingly, there is a need for an efficient low complexity decoding of finite-length irregular LDPC codes for ultra-high speed communications.